Who knew this 300,000-square-foot underground facility ever existed, but word comes from the United States Citizenship and Immigration Service (USCIS) that its National Records Center is turning 15 years old.

Located in Lee’s Summit, Mo., the center houses 20 million files on documented immigrants, each file one to six inches thick. Some 500 full-time employees and contract workers process 1.5 million files a year, according to USCIS Chief of Staff Juliet K. Choi, who recently visited the facility to mark its anniversary.

Employers and business owners, to understand your legal relationship to USCIS, get a copy of our I-9 Compliance Kit today. It covers all the details of ensuring your employees have been verified to have a legal right to work in the U.S.